|
Failed
Shock Absorber Caused ATV
Rollover?
Metallurgical failure analysis was requested of a
failed rear shock absorber bracket from a four-wheel
ATV involved in a fatal accident.
The failed shock absorber bracket was manufactured
from a cast aluminum alloy. An overall view of a
portion of the failed shock absorber bracket is
shown in Photograph A.
Photograph A:
Overall view of portion of failed shock absorber
bracket.
The failed shock absorber bracket fracture surface
shown in Photograph B contained a region of flat
fracture, denoted with arrows. A profile view of the
fractured shock absorber bracket, shown in
Photograph C, reveals that the casting fracture is
very straight and flat. The flatness of the fracture
surface is denoted in Photograph C with arrows
Photograph B: Photo of flat
fractured area of shock absorber bracket. Arrows
denote area of flat fracture.
Photograph C:
Profile view of flat fracture. Arrows denote area of
flat fracture.
Scanning electron microscopy (SEM) of the failed
casting fracture surface was conducted in the areas
denoted in Photograph D. The surface of the casting,
at a magnification of 14x, revealed considerable
casing shrinkage porosity. The casing porosity is
shown in the scanning electron micrograph in
Photograph E.
Photograph D:
Denoted areas examined by Scanning Electron
Microscope (SEM).
Photograph E:
Scanning Electron Micrographs at magnification (14X)
showing casting porosity.
A close-up view of the areas of casting porosity is
shown in Photograph F. The characteristic appearance
of shrinkage casting dendrites is clearly evident.
F
Photograph F:
Scanning Electron Micrograph at higher magnification
(200X) of casting porosity.
The fracture surface between the shrinkage porosity
exhibited a dimple rupture fracture surface, and is
shown in Photograph G. No evidence of metal fatigue
(as preliminarily indicated by the flat fracture)
was observed in the subject failed shock absorber
bracket.
Photograph G:
Scanning Electron Micrograph of surface between
shrinkage porosity exhibiting a dimple rupture
fracture surface (500X Magnification).
From the above studies, it was evident that the
failed ATV shock absorber bracket was not the cause
of the subject accident. The dimple rupture fracture
surface was the result of sudden impact, overload
failure.
Back to top
Back to
Recreational Vehicle Accidents
|
Dr.
R. Craig Jerner, Ph.D., PE specializes in accident
investigation and metallurgical failure analysis,
with over 30 years experience as a metallurgical
consultant and accident investigator. He has
testified as a metallurgical expert in over 250
depositions and more than 70 court appearances. If you or someone you know should need the services of Dr. Jerner and J.E.I. Metallurgical, please visit our web site at the buttons below, or e-mail Dr. Jerner --- 